There have been many attempts to devise an efficient, axially aligned rotary power device. One such device was described in U.S. Pat. No. 6,601,548, which issued to inventor Al-Hawaj on Aug. 8, 2003. This device describes an array of pistons arranged around a central shaft, with a system of roller cam followers to transmit power to the central shaft.
Inventor R. Driver in US published patent application 2002/20171 (published Feb. 21, 2002) describes a rotary power displacement fluid machine, with an eccentrically mounted central rotor and an array of axially-arranged vanes.
U.S. Pat. No. 5,209,190, issued on May 11, 1993 to inventor E. Paul, describes an open-ended hosing with a central rotor assembly and parallel cylinder elements around the central shaft.
Prolific inventor R. Duncan describes a rotary machine and thermal cycle in a series of U.S. Pat. Nos. 6,782,866, 6,684,825, 6,672,275, and 6,484,687, of issue dates Aug. 31, 2004, Feb. 3, 2004, Jan. 6, 2004, and Nov. 26, 2002. This device does not use a compressive piston stroke, but instead uses and expansion ring and gear to generate pressure.
US published patent application 2005/166,889 (published Aug. 4, 2005) describes a rotary device with coupled chamber halves and a drive disk plate.